In the control of engines, the conventional practice utilizes electronic control units having volatile and nonvolatile memory, input and output driver circuitry, and a processor capable of executing a stored instruction set, to control the various functions of the engine and its associated systems. A particular electronic control unit communicates with numerous sensors, actuators, and other electronic control units necessary to control various functions, which may include various aspects of fuel delivery, transmission control, or myriad others.
Early complex systems and subsystems which performed critical functions required separate control units which could promptly respond to dynamic vehicle situations and initiate appropriate actions. For example, a vehicle may have employed a brake controller, a cruise control module, a cooling fan controller, an engine controller, and a transmission controller, such that each vehicle system or subsystem had its own stand-alone controller. These controllers were either electronic control units or electronic circuits which may have had little or no communication among themselves or with a master controller. Thus, the vehicle was operated as a distributed control system, which often made it difficult to optimize overall vehicle performance by coordinating control of the various systems and subsystems.
As control systems became more sophisticated, the various distributed controllers were connected to communicate status information and coordinate actions. However, inter-controller communication delays were often unacceptable for critical control tasks, thus requiring independent processors or circuitry for those tasks. This expanded the overall capabilities of the control system and was often necessary to meet increasing consumer demands as well as more stringent emission control standards.
To meet these stricter standards, it has been necessary to expand the capabilities of the engine control system to more accurately control the engine operation. The complexity of the resulting control systems has often resulted in difficulty in the manufacturing, assembling, and servicing of vehicles. Manufacturers have attempted to decrease part proliferation, while increasing the accuracy of control, by combining increasingly more control functions into a single controller.
Advancements in microprocessor technology have facilitated the evolution of engine control systems. These systems began by implementing relatively simple control functions with mechanical apparatus, and progressed to more involved control schemes with dedicated controllers, before having matured as complex control strategies realized by a comprehensive engine controller. Many engine control systems found in the prior art address only a single subsystem control strategy and fail to capitalize on the advantages afforded by these microprocessor advancements. Another difficulty encountered by traditional, distributed engine control systems is the inability to protect the engine or engine components from system failures. Certain engine components, operated under extreme operating conditions, may fail.
The desire to provide application specific vehicles at a competitive price has led to the availability of a number of customer options which may include some of the systems already noted, such as vehicle speed control, engine speed control, or engine torque control. This in turn has led to a large number of possible subsystem combinations, thus increasing the costs associated with manufacturing and assembly as well as the cost of field service due to the large number of spare components which must be manufactured and stored.
It is desirable to have an electronic control unit capable of integrating the control of various engine functions and associated vehicle systems, thus eliminating inter-controller communication delays and harmonizing engine control with other vehicle subsystems. An additional benefit accrues from replacing independent stand-alone controllers with a comprehensive controller, to reduce part proliferation in the vehicle manufacturing, assembly, and service environments, leading to an associated reduction in the cost of these functions.
It is also desirable in optimizing overall vehicle performance, to have an electronic control unit which coordinates control of the engine with control of the transmission for smoother, more efficient shifting of the transmission. It is desirable to provide for throttle logic, and to provide for cylinder balancing to determine relative power contribution from each cylinder.
Due to increasing cost of fuel, it is further desirable to provide a controller which encourages certain driving techniques which enhance fuel economy. For example, it is desirable to provide an incentive to limit engine idling while the vehicle is stationary so as to reduce average noise levels and to reduce fuel consumption. It is further desirable to encourage the use of cruise control to minimize transmission shifting and increase overall fuel economy whenever possible.
It is also desirable to provide a controller which can control the engine in a manner which protects engine components during extreme operating conditions. For example, if a turbocharged vehicle is operated at high altitudes, the turbocharger will spin faster than a similar turbocharger operated at lower altitudes, and can be damaged.